Selective biosorption of U(VI) from aqueous solution by ion-imprinted honeycomb-like chitosan/kaolin clay composite foams

"Three-dimensional environment-friendly" amino acid functionalized chitosan: Uranium adsorption performance and mechanism research

To achieve the goals of "carbon peak and carbon neutrality" and sustainable development, we propose "Three-Dimensional Environment-Friendly" materials to balance the urgent need for the development of clean energy and the reduction of secondary environmental pollution during adsorbent preparation. In this study, three novel chitosan adsorbents (CMNSC-Leu, CMNSC-Pro, CMNSC-Phe) for uranium adsorption were designed on the basis of molecular level and successfully synthesized with three different amino acids (leucine, proline, phenylalanine) through amidation reaction in an aqueous environment using a sustainable green chitosan material. The uranium adsorption capacity of the three adsorbents was evaluated by batch adsorption, selectivity and recyclability studies. The adsorption reaction conformed to the pseudo-second-order model and was a spontaneous endothermic reaction. In particular, the maximum adsorption capacity of CMNSC-Pro for uranium was 462.7 mg·g-1 at C0 = 100 ppm. In addition, CMNSC-Pro showed better selectivity and good reusability. DFT calculation and IRI diagram were applied in this work to analyze the unique structure and adsorption process of CMNSC-Pro from the perspective of structure. Uranium was adsorbed by CMNSC-Pro via coordination, electrostatic interaction, and intraparticle diffusion. This work provided a new idea for the structural design and construction of new high-efficiency biomass adsorbents.

Encapsulation of Bamboosa vulgaris culms derived activated biochar into hierarchical permeable, phosphate rich and functionalized alginate aerogel composites and its contribution in U(VI) adsorption

In this study, a facile methodology was designed to encapsulate Bamboosa vulgaris culms derived activated biochar (BVC) in a variable mass ratio, into a three-dimensional hierarchical porous and permeable and amino-thiocarbamated alginate (TSC) to prepare hybrid biosorbents (BVC-MSA). These ultralight and lyophilized phosphate rich macroporous sorbents were rationally characterized through FTIR, XRD, BET, SEM-EDS, elemental mapping, XPS techniques and employed for efficient UO22+ adsorption from aqueous solutions. The phytic acid (PA) was found to be a suitable hydrophilic and phosphorylating agent for the TSC matrix through hydrogen-bonded crosslinking when employed in a correct mass ratio (1:3). The SEM-EDS and XPS analyses confirmed the UO22+ sorption onto BVC-MSA-3 (the most suitable composite with a BVC/TSC mass ratio of 30.0 % w/w) and provided evidence of heteroatom involvement in developing the physico-chemical interactions. The BCV-MSA-3 exhibited the best response as a sorbent during kinetics/sorption process, therefore, it was selected to study the equilibrium sorption studies. The BCV-MSA-3 removal efficiency increased from 12.1 to 94.2 % using 0.2 to 1.8 g/L sorbent dose at pH (4.5). The mentioned sorbent displayed a significant maximum sorption capacity qm (309.55 mg/g at 35 °C) calculated through the best-fitted Langmuir and Temkin models (R2 ≈ 0.99). The sorption kinetics followed the pseudo-second-order (PSORE) model and exhibited fast sorption rate teq (180 min). Thermodynamic parameters clarified that the sorption process is feasible ΔGo (-25.3 to -27.6 kJ/mol kJ/mol), endothermic ΔHo (27.17 kJ/mol), and proceeds with a positive entropy (0.176 kJ/mol.K). The study shows that BCV-MSA-3 could be an alternative and auspicious sorbent for uranium removal from aqueous solution.

Bis-substituted amino acid functionalized chitosan aerogels: High uranium adsorption capacity and antibacterial properties

Based on the goal of "carbon neutralization and carbon peaking", it is still challenging to develop a high adsorption performance and environmentally friendly material for uranium extraction. We proposed a new idea of "Three-Dimensional Environmental-Friendly". A series of amino acid bis-substituted chitosan aerogels (C-1, C-2, C-3, C-4 and C-5) were prepared by ice template method and selective substitution reaction in water environment. Among them, C-3 adsorbent has the antibacterial properties of gram-positive bacteria, gram-negative bacteria and marine bacteria, which is more suitable for uranium adsorption in complex environments. Also, C-3 adsorbent solves the shortcomings of poor adsorption property and easy to cause secondary pollution during modification of traditional chitosan materials. The selectivity and adsorption capacity of uranium are further improved by the unique functional groups of serine residues. At pH = 7, the maximum adsorption capacity reaches 606.32 mg/g. In addition, C-3 adsorbent have excellent selectivity and stability. The synergistic effect of coordination, electrostatic interaction and intraparticle diffusion between C-3 adsorbent and uranium may be the key to its high adsorption performance. The high performance of chitosan adsorbent provides a new idea for the design and application of green and efficient uranium adsorption materials.

Honeycomb-like macroporous crosslinked chitosan assisted EDTA-intercalated Ca-Mg-Al layered hydrotalcite composite foams for efficient U(VI) biosorption

The biosorption is considered to be highly efficient for the separation of radionuclide from radioactive wastewater. Herein, the crosslinked chitosan assisted EDTA intercalated Ca-Mg-Al layered double hydroxides composite foam (CS-EDTA-LDH) was synthesized by combining EDTA intercalation and freeze-drying methods. The macroporous and ultralight properties of CS-EDTA-LDH facilitates its rapid adsorption and facile recovery, and the inorganic/organic incorporation can avoid pore collapse and provide numerous adsorption sites, while the EDTA intercalation can enhance the complex capture of U(VI). The CS-EDTA-LDH presents various functional groups (carboxyl, hydroxyl and amino groups) for U(VI) adsorption, and the adsorption capacity for U(VI) reached 272.3 mg/g at pH 5.0 and 298 K. The adsorption kinetics of U(VI) conformed to PSO equation, whereas the isotherms conformed to the Freundlich model, indicating heterogeneous adsorption with diffusion process as a rate-controlling step. The thermodynamic parameters indicate that U(VI) adsorption by CS-EDTA-LDH is endothermic and spontaneous in nature. The adsorption mechanism is related to the synergic complexation by multi-functional groups, ion exchange, and possible isomeric substitution. Overall, CS-EDTA-LDH could be a promising biosorbent for the cleanup of radioactive pollution due to its high performance for U(VI) adsorption and facile recovery.

Antimicrobial ion-imprinted chitosan-derived hydrogel with quaternary ammonium and thermoresponsive components for UO22+ adsorption

Uranium recovery from wastewater or seawater is important for both pollution control and uranium supply. Due to the complexity of the water body, it requires that the adsorbent should not only be highly efficient for selective adsorption but also have good antimicrobial properties. In this study, an antimicrobial thermosensitive hydrogel (UITAC) for uranium adsorption was prepared by one-step ion-imprinted polymerization using chitosan as a substrate and allyl trimethylammonium chloride as the antimicrobial modifier. UITAC showed excellent antibacterial rate against Escherichia coli and Staphylococcus aureus, being 98.8 % and 89.1 %, respectively. Endothermic and exothermic peaks respectively showed up at 36.3-38.5 °C and 30.5-34.1 °C in the DSC curves. UITAC quickly achieved its adsorption equilibrium in 30.0 min at 50 °C, pH 5.0 in the 0.8 mg/mL UO22+ solution, with an adsorption capacity of 81.2 mg/g. The adsorption capacity could remain at 80 % after 5 cycles of repeated use. UITAC showed better adsorption selectivity to UO22+ than vanadium and other metal ions, with selectivity coefficients α(UO22+/Mn+) being 1.4-10.3. The pseudo-second-order kinetics and Langmuir adsorption model had a better fit for UO22+ adsorption by UITAC. The adsorption was a spontaneous process. The Gibbs Free Energy change, enthalpy change, and entropy change at 323.2 K were - 16.0 kJ/mol, 64.3 kJ/mol, and 248.4 J/mol·K, respectively. UITAC showed high potential in practical application environment.

Selective biosorption of Li+ in aqueous solution by lithium ion-imprinted material on the surface of chitosan/attapulgite

The extraction of Li+ from liquid lithium resources is a pivotal focus of current research endeavors. Attapulgite (ATP), characterized by its distinctive layered structure and inherent ion exchange properties, emerges as an exceptional material for fabricating lithium-ion sieve. Ion-imprinted chitosan/ATP composite materials are successfully synthesized, demonstrating efficacy in selectively absorbing Li+. The results emphasize the rich functional groups present in H-CTP-2, enhancing its absorbability and selectivity, with an adsorption capacity of 37.56 mg•g-1. The adsorption conforms to the Langmuir and pseudo-second-order kinetic model. Li+ coordination involves amino and hydroxyl group, indicating a chemisorption process. Furthermore, the substantial pore structure and significant specific surface area of ATP significantly promote Li+ adsorption, suggesting its participation not only in chemisorption but also in physical adsorption. The fabricated ion-imprinted materials boast substantial adsorption capacity, exceptional selectivity, and rapid kinetics, highlighting their potential for effectively separating Li+ from aqueous solution.

Ion-imprinted macroporous polyethyleneimine incorporated chitosan/layered hydrotalcite foams for the selective biosorption of U(VI) ions

In order to prevent uranium pollution and recovery uranium resources, it was necessary to find a highly efficient adsorbent for radioactive wastewater treatment. Herein, U(VI) imprinted polyethyleneimine (PEI) incorporated chitosan/layered hydrotalcite composite foam (IPCL) was synthesized by combining ion-imprinting and freeze-drying techniques. IPCL has a high amino/imino content and an ultralight macroporous structure, making it capable of efficiently adsorbing U(VI) and easy to separate; Especially after ion-imprinting, vacancies matching the size of uranyl ions were formed, significantly improving U(VI) selectivity. The adsorption isotherms and adsorption kinetics were in accordance with the Freundlich model and PSO model respectively, indicating that heterogeneous adsorption of U(VI) by the adsorbents. The adsorption capacity of IPCL-2 for U(VI) reached 278.8. mg/g (under the conditions of optimal pH 5.0, temperature of 298 K, contact time of 2 h, and adsorbent dosage of 0.2 g/L), which is almost double of that for the non-imprinted foam (PCL-2, 138.2 mg/g), indicating that IPCL-2 can intelligently recognize U(VI). The heterogeneous adsorption mechanism of U(VI) by IPCL-2 involves complexation, ion-exchange and isomorphic substitution. The adsorption of U(VI) by IPCL-2 is spontaneous and endothermic. IPCL-2 has excellent adsorption performance for U(VI), and is a promising adsorbent for radioactive pollution control.

Lawsonia inermis-organically modified chitosan intercalated bentonite clay: A multifunctional nanotheranostic system for controlled drug delivery, sensing and cellular imaging

This study presents the development of organo-bentonites (OBs); a cost-effective drug delivery system holding both sensing and imaging capabilities. The OBs were synthesized using quaternary ammonium cations derived from chitosan, Lawsonia inermis, and pyrene/anthracene carboxaldehyde combinations through a three-step process: Mannich reaction, quaternization, and intercalation. Physicochemical characterization confirms the organic modification of bentonite. The OBs: NQPB and NQAB hold substantial ciprofloxacin (Cipro) loading capacities (71.51 % and 78.04 %, respectively) and exhibit pH-dependent release profiles, suggesting their potential use as drug delivery platforms. Cell viability evaluation by MTT and live-dead assays indicates favourable results. Both OBs demonstrate fluorescence within the 450-500 nm range, and they display concentration-dependent fluorescence quenching and enhancement for NQPB and NQAB, respectively, in the presence of tryptophan (Trp), making them suitable for its detection. Confocal analysis further enunciates the live intracellular fluorescence upon OB uptake. In summary, the intrinsically fluorescent mesoporous OBs synthesized from Lawsonia inermis and chitosan exhibit multifunctionality, including Cipro delivery, Trp sensing, and live cell imaging. Among the OBs, NQAB could be considered as a promising theranostic platform owing to its superior cytocompatibility (>80 %), appreciable fluorescence, and controlled release profile.

High efficiency adsorption of uranium by magnesia-silica-fluoride co-doped hydroxyapatite

Hydroxyapatite has a high affinity to uranium, and element doping can effectively improve its adsorption performance. In this study, magnesia-silica-fluoride co-doped hydroxyapatite composite was prepared by hydrothermal method, and the effect of single-phase and multiphase doping on the structure and properties of the composites was investigated. The results showed that the specific surface area of Mg-Si-F-nHA composites increased by 63.01% after doping. Comparing with nHA, U(VI) adsorption capacity of Si-nHA, Mg-Si-nHA and Mg-Si-F-nHA composites increased by 13.01%, 17.39% and 22.03%, respectively. The adsorption capacity of Mg-Si-F-nHA composite reached 1286.76 mg/g. Adsorbent dosage and pH obviously affected U(VI) adsorption, and the experimental data can be fitted well by PSO and Sips models. The physicochemical characterization before and after adsorption suggested that complexation, ion exchange and precipitation participated in uranium adsorption. In conclusion, different elements doping can effectively improve the uranium adsorption properties of hydroxyapatite composites.

Macroporous and ultralight polyethyleneimine-grafted chitosan/nano-TiO2 foam as a novel adsorbent with antibacterial activity for the efficient U(VI) removal

The radioactive contamination from the excessive discharge of uranium-containing wastewater seriously threatens environmental safety and human health. Herein, macroporous and ultralight polyethyleneimine-grafted chitosan/nano-TiO2 composite foam (PCT) with antibacterial activity was synthesized, which could quickly remove U(VI) from solution. Among different PCT adsorbents, PCT-2 had the best adsorption performance for U(VI), which could be due to its honeycomb macroporous structures and the presence of abundant amino/imine groups. The kinetics and adsorption isotherms data were found in agreement with the pseudo-second-order model and the Langmuir model, respectively, indicating chemisorption or complexation as the main adsorption mechanism. The saturated adsorption capacity of PCT-2 for U(VI) reaches 259.91 mg/g at pH 5.0 and 298 K. The PCT-2 also presents good selectivity for U(VI) with the coefficient (βU/M) order of Na+ > K+ > Mg2+ > Ca2+ > Ni2+ > Co2+ > Mn2+ > Al3+ > Fe3+ > Cu2+. The adsorption mechanism was explored using FT-IR and XPS analysis, indicating that amino/imine groups and hydroxyl groups are responsible for U(VI) complexation. Thermodynamic calculations show that U(VI) adsorption is endothermic and spontaneous. The ease of preparation, excellent adsorption performance and environmental friendliness of PCT-2 make it a novel adsorbent with antibacterial activity for radioactive contamination control.

Synthesis and fabrication of segregative and durable MnO2@chitosan composite aerogel beads for uranium(VI) removal from wastewater

To address the imperative need for efficient removal of uranium-containing wastewater and mitigate radioactive contamination risks associated with nuclear energy, the development of materials with high removal efficiency and facile separation is crucial. This study designed and synthesised MnO2@chitosan (CTS) composite aerogel beads by in-situ growing δ-MnO2 on porous CTS aerogel beads. This approach not only mitigates the agglomeration of MnO2 nanospheres but also significantly enhances the porous structure and surface area of MnO2@CTS. These cost-effective and eco-friendly millimeter-scale spherical aerogels exhibited convenient separation properties after adsorption. These characteristics help mitigate the risk of equipment seam blockage and secondary pollution that are often associated with powdered adsorbents. Additionally, MnO2@CTS exhibited remarkable mechanical strength (stress approximately 0.55 MPa at 60 % strain), enabling rapid separation and easy regeneration while maintaining high adsorption performance even after five cycles. Significantly, MnO2@CTS exhibited a maximum adsorption capacity of 410.7 mg/g at pH 6 and 298 K, surpassing reported values for most CTS/MnO2-based adsorbents. The chemisorption process of U(VI) on MnO2@CTS followed the pseudo-second-order kinetic and Dubinin-Radushkevish models. X-ray photoelectron spectroscopy analysis further confirmed the reduction of U(VI) to U(V/IV). These findings highlight the substantial potential of MnO2@CTS aerogel beads for U(VI) removal from aqueous solutions, positioning them as a promising solution for addressing U(VI) contamination in wastewater.

Chitosan Hydrogels for Water Purification Applications

Chitosan-based hydrogels have gained significant attention for their potential applications in water treatment and purification due to their remarkable properties such as bioavailability, biocompatibility, biodegradability, environmental friendliness, high pollutants adsorption capacity, and water adsorption capacity. This article comprehensively reviews recent advances in chitosan-based hydrogel materials for water purification applications. The synthesis methods, structural properties, and water purification performance of chitosan-based hydrogels are critically analyzed. The incorporation of various nanomaterials into chitosan-based hydrogels, such as nanoparticles, graphene, and metal-organic frameworks, has been explored to enhance their performance. The mechanisms of water purification, including adsorption, filtration, and antimicrobial activity, are also discussed in detail. The potential of chitosan-based hydrogels for the removal of pollutants, such as heavy metals, organic contaminants, and microorganisms, from water sources is highlighted. Moreover, the challenges and future perspectives of chitosan-based hydrogels in water treatment and water purification applications are also illustrated. Overall, this article provides valuable insights into the current state of the art regarding chitosan-based hydrogels for water purification applications and highlights their potential for addressing global water pollution challenges.

Magnetite/β-cyclodextrin/fly ash composite as an effective and recyclable adsorbent for uranium(VI) capture from wastewater

As a novel adsorbent for the separation of uranium(VI) from wastewater, Magnetite/β-cyclodextrin/fly ash composite (Fe₃O₄/β-CD/FA) was first prepared via a chemical coprecipitation technology. The characterization results indicated that Fe₃O₄ and β-CD had been successfully loaded on FA, which had brought abundant oxygen-containing functional groups, providing numerous adsorptive sites for the removal of uranium(VI). At pH = 5.0 and T = 25 °C, the maximum uranium(VI) removal efficiency and capacity of Fe₃O₄/β-CD/FA were higher to 97.8% and 444.4 mg g^-1, respectively. Pseudo-second-order and Langmuir models fitted better with the experimental data, illustrating that chemical adsorption dominated the uranium(VI) removal process. In addition, Fe₃O₄/β-CD/FA showed good anti-interference ability and recoverability. After five cycles, the removal rate of uranium(VI) on Fe₃O₄/β-CD/FA was still higher to 90.4%. The immobilization of uranium(VI) on Fe₃O₄/β-CD/FA was mainly ascribed to the synergism of redox reaction, complex reaction, chemical reaction and electrostatic interaction. Given the above, Fe₃O₄/β-CD/FA would be regarded as an efficacious, green and promising adsorbent for uranium(VI) separation from wastewater.

A dual-functional fluorescent probe based on kaolin nanosheets for the detection and separation of aluminum ions

Aluminum ions (Al³⁺) are closely related to environmental protection and human health, thus the detection and separation of Al³⁺ is of great significance. In this study, a dual-functional fluorescent probe for the detection and separation of Al³⁺ was successfully developed by grafting fluorophore onto kaolin nanosheets. The probe has the characteristics of good dispersion without the involvement of organic solvents, excellent specificity, the low limit of detection (0.55 µM), and fast response time (10 min). And the recovery rates of Al³⁺ using this probe are in the range from 93.0% to 101.8%, and the corresponding relative standard deviations are in the range from 3.5% to 5.8%. Besides, it also can remove Al³⁺ in aqueous solution through adsorption, and the removal rates is in the range from 95.1% to 99.3% when the concentration of the probe is 0.4 mg/mL. The probe combines detection and separation functions, overcomes the defect that single-function materials can only be used for detection or separation, which has important significance and good application value.

Ion-Imprinted Polymeric Materials for Selective Adsorption of Heavy Metal Ions from Aqueous Solution

The introduction of selective recognition sites toward certain heavy metal ions (HMIs) is a great challenge, which has a major role when the separation of species with similar physicochemical features is considered. In this context, ion-imprinted polymers (IIPs) developed based on the principle of molecular imprinting methodology, have emerged as an innovative solution. Recent advances in IIPs have shown that they exhibit higher selectivity coefficients than non-imprinted ones, which could support a large range of environmental applications starting from extraction and monitoring of HMIs to their detection and quantification. This review will emphasize the application of IIPs for selective removal of transition metal ions (including HMIs, precious metal ions, radionuclides, and rare earth metal ions) from aqueous solution by critically analyzing the most relevant literature studies from the last decade. In the first part of this review, the chemical components of IIPs, the main ion-imprinting technologies as well as the characterization methods used to evaluate the binding properties are briefly presented. In the second part, synthesis parameters, adsorption performance, and a descriptive analysis of solid phase extraction of heavy metal ions by various IIPs are provided.

Selective removal of uranyl ions using ion-imprinted amino-phenolic functionalized chitosan

The recovery of uranium from aqueous effluents is very important for both the environment and the future of nuclear power. However, issues of sluggish rates and poor selectivity persist in achieving high-efficiency uranium extraction. In this study, uranyl (UO₂²⁺) ions were imprinted on an amino-phenolic chitosan derivative using an ion-imprinting method. First, 3-hydroxy-4-nitrobenzoic acid (HNB) units were joined to chitosan via amide bonding, followed by reducing the -NO₂ residues into -NH₂. The amino-phenolic chitosan polymer ligand (APCS) was coordinated with UO₂²⁺ ions, then cross-linked with epichlorohydrin (ECH), and finally the UO₂²⁺ ions were taken away. When compared to non-imprinted sorbent, the resulting UO₂²⁺ imprinted sorbent material (U-APCS) recognized the target ions preferentially, allowing for much higher adsorption capacities (q_m = 309 ± 1 mg/g) and improved adsorption selectivity for UO₂²⁺. The FTIR and XPS analyses supported the pseudo-second-order model's suggestion that chemisorption or coordination is the primary adsorption mechanism by fitting the data well in terms of kinetics. Also, the Langmuir model adequately explained the isotherms, suggesting UO₂²⁺ adsorption in the form of monolayers. The pH_ZPC value was estimated at around 5.7; thus, the optimum uptake pH was achieved between pHs 5 and 6. The thermodynamic properties support the endothermic and spontaneous nature of UO₂²⁺ adsorption.

The preparation of dodecyl trimethyl ammonium bromide modified titanium dioxide for the removal of uranium

Radioactive contamination, especially the uranium pollution, is threatening the ecological environment. How to efficiently and quickly remove uranium from the environment is a problem to be solved. Herein, the dodecyl trimethyl ammonium bromide embellished titanium dioxide (DTAB/TiO₂) was prepared as an adsorbent to adsorb uranium (U) from water. The introduction of dodecyl trimethyl ammonium bromide can improve the adsorption capacity of titanium dioxide for U(VI). Besides, the excellent chemical stability of DTAB/TiO₂ would not result in secondary pollution, which was the novelty of this work. The DTAB/TiO₂ composite was composed of nanoparticles and presented a spherical morphology with a rough surface. The radius of DTAB/TiO₂ was 0.45 μm, and the specific surface area reached 144.0 m²/g. The removal of U(VI) on DTAB/TiO₂ was a monolayer adsorption process, and the removal process was dependent on the solution pH. The capture of U(VI) improved with the temperature increase, indicating an endothermic process. The adsorption process can reach equilibrium within 240 min. Based on the Langmuir model, the adsorption capacity of DTAB/TiO₂ for U(VI) reached 108.4 mg/g. The surface oxygen-containing functional groups, especially hydroxyl groups, played a crucial role in removing U(VI). This work can provide useful information for the cleanup of uranium and expand the application of surfactants.

Highly efficient adsorptive extraction of uranium from wastewater by novel kaolin aerogel

An environment-friendly, low-cost and efficient kaolin aerogel adsorbent (named as KLA) was synthesized via a freeze-drying-calcination method to solve the defect of low uranium removal rate for kaolin (KL). The removal rate of uranium on KLA reached 90.6 %, which was much higher than that of KL (69.2 %) (C₀ = 10 mg L^-1, t = 24 h, pH = 5.0, T = 298 K and m/V = 1.0 g L^-1). The uranium removal behavior on KLA was satisfied with Pseudo-second-order and Langmuir model, which meant that the uranium ions were immobilized on the surface of KLA via chemical reaction. Meanwhile, high temperature was in favor of the removal of uranium on KLA, indicating that the removal process was a spontaneous endothermic reaction. Compared with KL, KLA also presented better cycle ability and its removal rate of uranium was up to 80.5 % after three cycles, which was still higher than that of KL at the first cycle (74.5 %). On basis of the results of SEM, XRD, FT-IR and XPS, it could be concluded that uranium ions were adsorbed by KLA via complexation. Hence, KLA could be regarded as a feasible candidate for the removal of uranium from aqueous solution.

Polyethyleneimine incorporated chitosan/α-MnO2 nanorod honeycomb-like composite foams with remarkable elasticity and ultralight property for the effective removal of U(VI) from aqueous solution

The development of new adsorbents is needed to address the environmental challenges of radioactive wastewater treatment. Herein we reported a novel polyethyleneimine incorporated chitosan/α-MnO₂ nanorod honeycomb-like composite (PCM) foam with remarkable elasticity and ultralight property for U(VI) removal. Among different PCM sorbents, PCM-40 possessed the highest sorption capacity for U(VI) due to its highly developed macroporous structure and high content of amine/imine groups. The kinetics were well-simulated by the pseudo-second-order model, indicating chemisorption as the rate-controlling step. The isotherms could be described by the Langmuir model, suggesting mono-layer homogeneous sorption of U(VI). The maximum sorption U(VI) capacity for PCM-40 reaches up to 301.9 mg/g at pH 4.5 and 298 K. The thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. The main sorption mechanism is related to the complexation of uranyl ions with the amine/imine and hydroxyl groups. The high sorption capacity, fast kinetic rate and relatively good selectivity of PCM-40 highlights its promising application in radioactive pollution cleanup.

Synthesis of a New Chelating Iminophosphorane Derivative (Phosphazene) for U(VI) Recovery

A new synthetic chelating N–hydroxy–N–trioctyl iminophosphorane (HTIP) was prepared through the reaction of trioctylphosphine oxide (TOPO) with N–hydroxylamine hydrochloride in the presence of a Lewis acid (AlCl₃). Specifications for the HTIP chelating ligand were successfully determined using many analytical techniques, ¹³C–NMR, ¹H–NMR, FTIR, EDX, and GC–MS analyses, which assured a reasonable synthesis of the HTIP ligand. The ability of HTIP to retain U(VI) ions was investigated. The optimum experimental factors, pH value, experimental time, initial U(VI) ion concentration, HTIP dosage, ambient temperature, and eluents, were attained with solvent extraction techniques. The utmost retention capacity of HTIP/CHCl₃ was 247.5 mg/g; it was achieved at pH = 3.0, 25 °C, with 30 min of shaking and 0.99 × 10⁻³ mol/L. From the stoichiometric calculations, approximately 1.5 hydrogen atoms are released during the extraction at pH 3.0, and 4.0 moles of HTIP ligand were responsible for chelation of one mole of uranyl ions. According to kinetic studies, the pseudo–first order model accurately predicted the kinetics of U(VI) extraction by HTIP ligand with a retention power of 245.47 mg/g. The thermodynamic parameters ΔS°, ΔH°, and ΔG° were also calculated; the extraction process was predicted as an exothermic, spontaneous, and advantageous extraction at low temperatures. As the temperature increased, the value of ∆G° increased. The elution of uranium ions from the loaded HTIP/CHCl₃ was achieved using 2.0 mol of H₂SO₄ with a 99.0% efficiency rate. Finally, the extended variables were used to obtain a uranium concentrate (Na₂U₂O₇, Y.C) with a uranium grade of 69.93% and purity of 93.24%.